1. Field of the Invention
The present invention relates generally to a vehicle seat and more specifically to a suspension arrangement for a vehicle seat the hardness characteristics of which can be automatically adjusted in accordance with road conditions, vehicle operational parameters and the like.
2. Description of the Prior Art
FIGS. 1 and 2 shows a previously proposed suspension arrangement used to support a seat in a vehicle cabin or the like. This arrangement is disclosed in detail in British patent specification No. 1,230,734. As shown, a pair of springs 2,2 and a pair of dampers 4, 4 are disposed in a seat frame which is arranged essentially horizontally with respect ot a frame or base. One end of each of the springs 2, 2 and dampers 4, 4 is secured to a transverse connecting member 6 which extends between two pair of scissor levers 8. The other ends of the dampers 4, 4 are connected to the seat frame 10 while the other ends of the springs 2, 2 are connected with a lever arrangement 12 which permits the tension in the springs to be adjusted. This arrangement, while permitting a very compact construction which can be readily applied to a reclining seats, has suffered from the drawback that as the springs 2, 2 and the dampers 4, 4 are operatively interconnected in a manner which permits the same to act directly against one another, the damping period of the system tends to be excessively long thus permitting the seat to oscillate up and down in a manner which imparts a disturbingly unstable sensation to the occupant. Also, the arrangement cannot be adjusted in a manner which selectively varies the hardness of seat suspension characteristics.